The washing program of a program-controlled dishwashing machine comprises several cleaning and rinsing processes which are completed with a clear rinsing process. In this case, a clear rinsing liquid provided with a clear rinsing agent is supplied to the cleaned crockery located in the washing container. The clear rinsing agent is frequently metered by the customer, in which case, however, the adjusted quantity is merely a rough value. On the one hand this can therefore result in overdosing and an unnecessarily high consumption of clear rinsing agent. If the dosing is inadequate, on the other hand, the desired clear rinsing effect is frequently not achieved. Manual dosing of the clear rinsing agent also cannot take into account the quality of the clear rinsing agent used.
Alternatively, so-called “3-in-1” combination preparations have been available for some time for use in dishwashing machines, these comprising a cleaning substance, a softening substance and a clear rinsing substance and being supplied simultaneously to the washing container of the dishwashing machine at a specific time. The combination preparations are available in compressed tablet form (so-called “tabs”) and also in powder form. They can be inserted in dosing devices provided in the dishwashing machine. In this case, they are added to the washing container at a particular time which is determined by the washing program sequence of the dishwashing machine.
However, the known “3-in-1” combination preparations have the disadvantage that they dissolve differently depending on various parameters and accordingly have their highest efficiency at different times. For example, there are combination preparations which work according to a so-called “dilution principle”, i.e. the combination preparation is added at the beginning of the cleaning process and begins to dissolve. In this case, the clear rinse agent is initially added in a high concentration, i.e., overdosed and it is assumed that as a consequence of entrainment in washing water residues and adhesion of the dissolved clear rinse agent on the items to be washed, on the walls of the washing container and also in the supply pipes, the concentration in the clear rinsing process is still sufficient to achieve a good drying result. However, combination preparations of this type have the disadvantage that when a plurality of washing program sections are carried out before the clear rinsing process, the combination preparation dissolves too quickly and as a result of the repeated change of rinsing liquid, said preparation is no longer present in sufficient concentration in the actual clear rinsing process.
Other combination preparations are designed so that initially only the cleaner and the softener dissolve and the clear rinse agent which is encapsulated in the combination preparation, e.g. in the form of a wax-sheathed pearl, only dissolves during the clear rinsing depending on the temperature and/or the pH. However, when using a washing program which already operates at high temperatures in the cleaning program section and/or where the duration of the cleaning process is selected to be very long, the clear rinse agent is already dissolved before the actual clear rinsing process.
To solve the problems described above, DE 102 57 826 A1 provides the use of at least one optical sensor which can detect the type of combination preparation used. Changes in concentration and/or pH and/or variations in the degree of hardness of the rinsing liquid are detected, allowing conclusions to be drawn on the concentration of the individual active substances.
In order to be able to encounter a particular concentration of clear rinsing agent in the clear rinsing process step, a defined volume of rinsing liquid is supplied to the washing container. This can be fixedly determined in advance or adjusted in a variable manner depending on various parameters. The concentration of the clear rinsing agent actually present in the rinsing liquid is used as an important quantity since this directly influences the clear rinsing result and therefore the drying result of the items to be washed. If the concentration of clear rinse agent at the beginning of the clear rinsing program section is low, as little rinsing liquid as possible is added, optionally depending on the degree of turbidity of the rinsing liquid. On the other hand, if the concentration of clear rinsing agent at the beginning of the clear rinsing program section is above-average or sufficiently high, the concentration of the clear rinsing agent can be adjusted to a pre-determined concentration by supplying a definedly adjustable volume of rinsing liquid.
In order to prevent overdosing of clear rinsing agents, DE 100 45 151 C2 proposes that the foam concentrations of the clear rinsing liquid is monitored by means of an optical sensor and compared with a set point for the foam concentration. When the predefined set point of the foam concentration is reached, the supply of clear rinsing agent is automatically reduced.
Furthermore, DE 100 34 546 A1 proposes the use of a radar sensor to determine the droplet size or shape or the status data of a test body wetted with the rinsing liquid in order to make predictions on the state of the rinsing liquid, for example, its content in the rinsing liquid.